Peter Sinclair has video interview with Andrew Dessler about water vapour and climate. The video doesn’t really say anything all that surprising. We are now reasonably sure that relative humidity remains roughly constant as we warm. This then allows us to constrain the role water vapour and indicates that it will have a net positive effect (it will amplify warming). Clouds are still uncertain, mainly because they can both reflect incoming radiation, cooling the climate, and trap heat, so warming the climate. However, our current understanding is that the net effect is probably that clouds will be a net warming influence.
The real reason I wanted to post the video was to make a slightly different point. Given the above, we have a number of lines of evidence indicating that the equilibrium climate sensitivity (ECS) is probably greater than 2oC. This includes paleo estimates, climate models, but also our basic understanding of the physical processes involved.
As many are aware, there are, however, some studies that suggest that ECS is probably less than 2oC. Many of these are methods that rely on statistical analyses of observations. There is, of course, nothing wrong with these methods, but simply because someone has correctly applied a statistical technique, does not mean the result is correct (or correctly represents reality).
The key point I was wanting to highlight is that if some really think that ECS is probably less than 2oC, then at some point someone is going to have to illustrate what physical processes are involved. At the moment, our understanding is that the various processes involved (clouds, water vapour, lapse rate, …) suggest that the ECS is more likely above 2oC than below. No amount of complicated statistics trumps this kind of understanding.